Petroleum or synthetic hydrocarbons solvents as well as natural terpene hydrocarbon solvents or mixtures thereof, with or without other modifier additives, were recently reconsidered and commercialized as long-term alternative cleaning agents for the widely used, but gradually being phased out, chlorofluorocarbons (CFCs) (example 1,1,2-trichloro-1,2,2-trifluoroethane) and other halogenated solvents such as dichloromethane, carbon tetrachloride, 1,1,1-trichloroethane, 1,1,2-trichloroethylene and perchloroethylene. These solvents are used in cleaning fluxes from printed circuit boards (PCBs) and cleaning of various machine oils used in the manufacture of different metallic and non-metallic components (degreasing/vapor degreasing processes) as well as for cleaning other contaminants such as particulates, buffing, polishing, lapping compounds, waxes, paints. The CFCs and the halogenated solvents are known to deplete the stratospheric ozone layer.
Ozone depletion leads to increasing the infiltrated ultraviolet radiation, which in turn increases potential incidents of cataracts, skin cancers and other human and ecological problems. The global consensus on an accelerated phaseout of materials with ozone depleting potential (ODP) is mounting. It has culminated recently in the "Montreal Protocol on Substances that Deplete the Ozone Layer" and in the revisions to accelerate the time limit for ending their production.
The cleaning process using CFCs (or their azeotropic mixtures with protic solvents) or chlorinated solvents involves immersing the components to be cleaned in the solvent which is heated and ultrasonically cavitated for certain period of time. Then, the components are exposed to solvent vapor for secondary cleaning and rinsing. Following this step, the components are removed and left to air dry. The CFCs and some chlorinated solvents have two main advantages in this process because they are non-flammable and volatile at ambient or low temperature. Thus, drying of the components is not problematic. Also, some CFCs were commonly used to dry some aqueously cleaned surfaces through surface water-film displacement in a drying machine known as the CFC dryer.
In contrast to CFCs, and halogenated solvents, water immiscible petroleum, synthetic and/or natural terpene hydrocarbons or hydrocarbons modified with other additives or surfactants are increasingly used as alternative sources for the cleaning of metallic and non-metallic surfaces. However, these solvents are always accompanied with rinsing and drying problems. Briefly, the cleaned surfaces are difficult to rinse and to dry and consequently, require prolonged drying times and relatively high temperatures. Drying of these solvents at high temperatures is associated with potential fire or environmental hazards, particularly those with low flash point solvents. Similar problems have also been found for surfaces cleaned with other water immiscible non-halogenated solvent cleaners including medium-high molecular weight alcohols, ethers, amines, esters and derivatives or mixtures.
The above identified problems are attributed to the inherent properties of these hydrophobic solvents and circumstances related to their uses. For example, rinsing or displacement of surfaces cleaned with these solvents is difficult because of their inherent lower surface tension. Furthermore, these non-halogenated solvents tend to leave a very thin organic film, after cleaning and drying, absorbed on the surfaces which negatively interferes in many cases with the next step in a multi-step surface preparation such as coating, etching or vacuum coating deposition. Also, in some instances the cleaning solution contains surfactants which tend to undesirably emulsify the hydrocarbon solvent on rinsing with water in order to remove it, rendering phase separation of the solvent unfeasible for subsequent collection and recycling.
It has been shown that several water rinse steps using plural rinses, following a cleaning step with either water-immiscible or water-emulsifiable or dispersable non-halogenated solvent cleaners at different temperatures, failed to completely remove the undesirable residue of the organic solvents in the relatively short time which is demanded by typical production requirements. The incomplete removal of the water-immiscible non-halogenated solvent film therefore renders many metallic and non-metallic surfaces, undesirably, water repellant or hydrophobic.
Complete removal of the non-halogenated or hydrocarbon base solvent residues is essential, particularly in cleaning and drying of metals and non-metals with different configurations that are manufactured to be used in the electronic industry. Also, subsequent processes such as etching, plating, coating, vacuum vapor deposition or painting require water break-free or hydrophilic surfaces to produce good results. Otherwise, the surface may suffer differential etching or coat adhesion problems respectively. Furthermore, a partially hydrophobic surface tends to repel the rinse water leaving water droplets on the surface which may dry in place leaving residual marks on drying. Moreover, the residual un-rinsed non-halogenated solvent may contain some of the original surface contaminants. On the other hand, a water break-free surface drains the rinse water faster and requires less energy and time to dry.
Metallic and non-metallic substrates which were first cleaned with a water immiscible (or partially water emulsifiable), heated, hydrocarbon base or non-halogenated solvent concentrate, by immersion in ultrasonically cavitated bath or which were submerged sprayed or simply dipped in with vertical or horizontal oscillation or rotation followed by rinsing with water, or a water diluted emulsion of the same hydrocarbon or non-halogenated solvent, ultrasonically cavitated, or sprayed or submerged sprayed followed by multi water rinses, failed to produce surfaces which are entirely free from the hydrophobic solvent residues. These residues may leave an undesirable residual odor of the natural or non-halogenated or petroleum hydrocarbon solvent or included additives; or interfere with the next step in a manufacturing operation process as mentioned above. Furthermore, the residual hydrocarbon or non-halogenated solvent with low flash point may create a fire-hazard if enough accumulates in the drying step which commonly uses recycled heated air. Air or inert gas drying techniques of those solvents require expensive and complex safeguards against fire hazard and to minimize their vapor release to the environment.
It is therefore highly desirable to have an improved process and aqueous composition for the cleaning and drying of metallic and non-metallic surfaces which overcomes the above-noted drawbacks resulting from the incomplete removal of the hydrocarbon or non-halogenated solvent. The present invention diminishes the potential for a fire-hazard or an explosion, as well as reduces the drying time by effectively removing the non-halogenated organic solvent residues or other flammable water-immiscible cleaning solvents. Furthermore, the invention diminishes the drag-out or carry over of these solvents on parts, therefore, allows efficient and economic rinse-water recovery through closed loop purification systems. Typical purification systems include activated carbon to remove organic residues. The carbon has certain loading capacity for organics before exchange or disposal.
Prior art related to the process and composition for the cleaning and drying of various surfaces has been disclosed in several patents. U.S. Pat. No. 5,041,235 describes a cleaning composition to clean porous surfaces containing a low molecular weight alcohol, synthetic hydrocarbon oil and a surfactant. U.S. Pat. No. 5,031,648 describes a spray method to clean mill gears soiled with gear lubes, greases and hardened residues with a composition containing a terpene hydrocarbon, aliphatic hydrocarbon solvent, surfactants, extreme pressure additive, thickeners and co-solvent followed by rinsing with a water-emulsifier soap solution in a pressure washer. U.S. Pat. No. 5,011,620 describes a cleaning composition of dibasic ester solvent and hydrocarbon solvent for cleaning flux residue from a printed circuit board. U.S. Pat. No. 4,983,224 describes a cleaning composition of terpenes/terpenols and polar aprotic solvents and a surfactant for cleaning fluxes. U.S. Pat. No. 4,877,556 discloses a cleaning composition of ethoxylated fatty alcohol, fatty acid ester, a monohydric alcohol, and liquid hydrocarbon for pretreatment of soiled fabrics before washing. U.S. Pat. No. 4,859,359 describes a composition which imparts water repellency to hard surfaces. The disclosed composition comprises a solvent mixture of glycol ether, a lower aliphatic alcohol, a hydrocarbon solvent and organic polysiloxane. U.S. Pat. No. 4,704,225 and Re. No. 33,210 describe a cleaning composition of terpene hydrocarbon, and a coconut oil fatty acid alkanolamide (an emulsifier) having water dispersed therein, water-in-oil emulsion.
There is no disclosure in the above-noted patents which would tend to suggest or otherwise provide motivation for employing a water-immiscible solvent cleaner followed by a solvent displacement/cleaning step, before the water rinsing step, which utilizes a biodegradable and environmentally benign, aqueous composition capable of producing hydrophilic surfaces and also phase separates the water-immiscible solvent for recovery or recycling, and expedites the drying of the cleaned parts.